In many installations in the upstream or downstream oil and gas industry, chemical and petrochemical industry, it is required to introduce a mixture of liquid and gas into a processing vessel. The vessel can be a separation vessel designed to separate the stream, e.g. a natural gas stream comprising oil and/or water, into liquid and gas streams. The vessel can also be a gas/liquid contacting vessel in which gas and liquid are counter-currently contacted to exchange heat or matter. An example of such a gas/liquid contacting vessel is a fractionation or distillation column, and a particular example is a vacuum distillation column.
In the specification and in the claims the word ‘gas’ is used to refer to gas and to vapour.
In order to introduce a mixture of gas and liquid into a column or vessel, so-called inlet devices are used. There are different types of inlet devices, varying in complexity and performance. Some inlet devices comprise or essentially consist of a splash plate, which is arranged in the flowpath of the mixture that flows into the column via an inlet nozzle. The splash plate breaks the momentum of the inflowing stream, and guides and deflects fluids laterally, to achieve some distribution of the inflowing mixture in the column.
Other inlet devices are designed such that a substantial (pre-)separation of liquid and gas is achieved, in particular employing centrifugal force on curved guiding vanes.
British patent specification No. 1 119 699 discloses a particular fluid inlet device for introducing a mixture of liquid and gas into a distillation column.
The known fluid inlet device comprises an inlet flow channel having an inlet end for receiving the mixture of liquid and gas, and a plurality of curved guiding vanes placed one behind the other along the inlet flow channel, wherein each vane comprises an intercepting part extending towards the inlet end of the inlet flow channel, and an outwardly directed deflecting part. The intercepting and deflecting parts of each vane are arranged in such a way that the vane intercepts and deflects part of the mixed feed stream, and is capable of effecting a separation between liquid and vapour by inertia and centrifugal force.
During normal operation a mixture of gas and liquid is supplied to the inlet nozzle of a column, which is in fluid communication with the inlet end of the inlet device. The vanes are curved so as to deflect the mixture outwardly. The change in the direction of flow causes a (pre-)separation of the mixture in that liquid is forced onto the concave surface of the vane thereby forming a liquid-rich film streaming on the concave surface, and a gas-rich stream in the remainder of the outlet channel between two vanes. After the streams have left the outlet channel, the liquid-rich stream moves downwards in the column under the influence of gravity, whereas the gas-rich stream flows upwards in the column. In a specific embodiment of the known device a liquid catching channel is arranged at the trailing rim of the vane perpendicular to the main flow direction along the vane. This channel serves to discharge all of the liquid that is separated by the vane sideways, i.e. perpendicular to the main flow direction.
Another inlet device with curved guiding vanes is for example a so-called vapour horn, e.g. as shown in the brochure “Internals for packed columns” with Number 22.51.06.40-III.06-50, by Sulzer Chemtech, on page 18 as GITV Cyclon inlet. In a vapour horn, the fluid mixture is introduced tangentially into the column, and a curved inlet flow channel extends along the inner circumference of the column. Curved guiding vanes along the curved channel pre-separate and deflect parts of the mixture towards the centre of the column.
The same page 18 in the Sulzer brochure also shows a GDP Splash plate inlet device and a GIV vane inlet device.
Yet another inlet device with curved guiding vanes is known from International Patent application with publication No. WO 03/070348.
An important parameter of a flow inlet device is the total remaining liquid entrainment in the gas, i.e. the remaining liquid content of the gas flowing into the column or vessel, typically upwards. In inlet devices including a guide member such as a splash plate or in particular a curved guiding vane, a smaller or larger part of the liquid content is precipitated onto the guide member and flows on a surface of the guide member into the column. However, part of the already separated liquid is re-entrained, which re-entrainment occurs generally in the region where gas and liquid streams leave the inlet device.
Re-entrainment is a general concern, including in distillation and separation applications, since it presents a larger liquid load to downstream equipment. Re-entrainment lowers the overall separation efficiency of the inlet device, since liquid that was already separated on the concave side of the vane, and that should ideally find its way towards the bottom of the vessel, is still carried upwardly with the gas. Generally, re-entrainment is expected to increase at high velocities, which are e.g. the consequence of minimization of vessel size in view of cost and area occupied, e.g. on an offshore installation.
It is desired to be able to operate with lower entrainment than possible with present inlet devices.